We usually use Unetbootin to create a bootable thumb drive from a Linux ISO, but it turns out you don't even need a thumb drive if you want to boot the live CD on the same computer that has Unetbootin installed. To do so, just start up Unetbootin and navigate to your disk image as normal, but instead of USB drive, just choose "Hard Disk" from the "Type" dropdown as shown above. Leave / for the Drive entry. Hit OK and when it's done, reboot your computer. GRUB should show a new "Unetbootin" entry that will boot you into your live environment—no blank CD or thumb drive required.

The next time you boot up Unetbootin it will ask you "remove the existing version of Unetbootin". This won't uninstall the program; it'll just remove its GRUB entry, so hit OK (unless you want to keep it there).